A particular method is today favoured for producing certain metal parts for aircraft turbo-engines; it resides in a method of selectively melting a powder using a directed beam, of laser beam or electron beam type. Such a method is known under the names of Direct Metal Laser Sintering, Selective Laser Melting or Electron Beam Melting.
Such a method consists in producing a metal part by melting successive layers of powder using a laser beam or using an electron beam commanded by an information processing system in which has been recorded the three-dimensional coordinates of the points of the successive layers to be formed. In a practical manner, in a vessel, the bottom of which is formed by a translationally moveable plate, is arranged a first powder layer by means of a scraper or a roller. The layer then has a lower surface corresponding to the surface of the plate and an upper surface on which is directed and moved the laser beam or the electron beam. The energy supplied by said beam causes local melting of the powder which, on solidifying, forms a first layer of the metal part. After formation of this first layer, the plate is lowered by a distance corresponding to the thickness of a layer, then a second powder layer is brought by the scraper onto the preceding layer. In the same manner as previously, a second layer of the metal part is formed by means of the beam.
These operations are repeated up to the complete production of the part.
Such a production method makes it possible to significantly shorten the times and the costs of developing metal parts thereby produced.
However, for metal parts having portions of relatively large thickness, such a production method remains slow: in fact, each of the different successive layers has a thickness comprised between twenty and one hundred micrometers, and the number of passages of the energy source of laser beam or electron beam type is thus high.
The production time of certain parts, for example the sections of high pressure and/or low pressure turbines, is thus dependent on parameters such as the scanning speed of the beam, its power, the thickness of each of the superimposed layers, the coverage rate of the passages of the laser . . . . This production time may attain eighty-five hours.
Furthermore, a liquid bath forms during the interaction between the laser or electron beam and the bed of powder; said liquid bath is, during the production process, relatively agitated, and it is frequent that particles or ejections are ejected from said liquid bath. Said particles or ejections then fall back onto the surface that has to undergo the following passage of the beam, which can be the source of production defects, defects capable of directly impacting the mechanical strength of the part. Such ejections are favoured by an important number of passages of beam over a same area.
In order to try to provide a solution to the problems that have been mentioned, different solutions have been proposed in the prior art.
A first solution resides in the production of metal parts by machining from a block of material; but within the framework of the development of these parts, during which their geometry is capable of being frequently modified, such a solution is not suitable; it would then in fact be necessary to adapt, for each of the considered parts, in particular the machining cycle and the tools for positioning the part.
A second solution consists in producing the part by founding. Such a solution may prove to be interesting uniquely for parts produced in large numbers, because the mould to use is very costly. Such a solution is absolutely not viable within the context of the development of a turbo-engine during which the geometry of the considered parts may constantly evolve.